Process of crystallization of wax



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2 Sheets-Sheet 1 INVENTOR far/P2777 BY j/da E ,JC

A TTORNE Y.

Dec. 19, 1933. E. PE1-TY PROCESS OF CRYSTALLIZATION 0F WAX Filed sept. 9, 1932 2 Sheets-Sheet 2 INVENToR far'/ Pe ffy LZ.

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ATTORNEY.

Patented .Dec. 19, 1933 ,UNITED -sTATEs 1,940,015 PROCESS F CRYSTALLIZATION WAX Earl Petty, Hempstead,

Products, Incorporated poration of Delaware Application September 9,

Nr'Y., assignor to Alca New- York, N. Y., a cor- 1932. Serial No. 832,278

7 Claims. (C1. 19(6-18) My invention relates to a process of crystallization of wax or more particularly to a method of dewaxing in which crystallization is controlled and chilling is accomplished by the aid .5 of a diluent-solvent.

The method of dewaxng in which a solventdiluent is used is known tojtheart. By thismethod a solvent, suchl as Vnaphtha is mixed With the oil to be dewaxed. Both the oilA componentand the wax component of the hydrocarbon oil are'soluble in the solvent. When the solution is chilled, the oil remains soluble. As the chilling progresses, wax crystals form ,and a portion of the wax component of thev solvent is thrown olI, thereby, upon crystallization. Inasmuch as the oil remains soluble, the excess o f the diluent goes to the oil. A sudden increase in the rate of crystal formation takes place at a certain temperature, depending upon the type 'of solvent used, the amount of solvent and the type of hydrocarbon oil. This lpoint is vusually termed the peak of crystallization, When the peak of crystallization is reached, a large amount of diluent is freed. Some waxes in the oil are always in a retarded state. The presence 'of an vexcess of diluent further retards these waxes. At the peak of crystallization and A at the same time as the shift of partition causing excess solution, there is the heat of crystallization to be removed; otherwise further re-` tardation or redissolving of wax will take place. In conventional processes the chilling curve or rate actually llattens out during the peak of crystallization when `the refrigeration input is constant. The excess of free diluent mayv even redissolve a portion of the wax crystals. In order to obtain complete crystallization, it is necessary to continue chilling the oil luntil another shift of the solvent takes place due to the reaching of a second peak of crystallization,

' at which point substantially all of the crystalline wax will be crystallized.

The fundamental problem of dewaxing is crystallization, whether it is to be handled asl crystalline, intermediate or amorphous wax by the extraction process.- I'he handling of crystalline waxes is lmost favorable from a commercial standpoint. Heretofore preparation for dewaxing has been the practice ol' crystallization by time, refrigeration, and selection of solvent which is used as a diluent only. From fundamental viewpoint the preparation of any crystal involves time, temperature and concentration of the solution or mother liquor. The manipula- `tion of all these features is practiced in most chemical processes where crystals are to be developed and removed. This case makes possible the use of all these features by theselection of a novel diluent which with the oil forms the mother solution.' The peculiarities and special y60 characteristics of the diluent are such that by pressure-temperature control and regulation it can be removed fromA the solution at any stage of the chilling and crystallization process and thereby elect the control of the concentration and bring about togetherl with refrigeration a more perfect crystallization. This cannot be done with the conventional solvents in the present day practices of preparing wax bearing,r oils for dewaxing. In removing the diluent-solvent the reduction of temperature is incidental and not a lprimary feature of my process since the temperature can or could be produced by indirect refrigeration and accomplish the results of my process.

According to the processor my invention, I propose to remove the solvent as it is thrown ci by the wax component, due to the formation of crystals. In other words, I contemplate chilling and preventing the presence of an excess of diluent and the attending retardation of crystallization and/or the redissolving of any crystalline wax which has. been formed. To do this effectively, I find it preferable to use a` diluentsolvent which is readily removablebyevaporation. For this purpose, I prefer to use propane. By propane, it is to be understood that any equivalent solvent having a boiling point falling between --65 F. and 32 F. is contemplated.V Such hydrocarbons as butane, iso-butane, or mixtures thereof,leither alone or with propane, would be elective in my process. It is possible to use ethane, though this has a lower boiling point than is necessary, or admixtures of such compounds as acetone, or other chemical compounds which would serve as crystal accelerators and still if used in admixtures in quantity and proportions with propane would not aiect the operation of my process since the removal of any constituent from the solvent or mother liquor will serve to reduce the concentration and accelerate precipitation.

It will-be appreciated that as propane is evaporated \not.only is the excess diluent removed but also chilling is produced, but this later result is incidental and the temperature can be reduced articially or indirectly and not alect my process.

One object of my ,invention is to provide a preparatory system of crystallization of wax whereby substantially complete crystallization is achieved at a higher temperature than has heretofore been possible.

Another object of my invention is to provide a method of crystallization or chilling preparatory to dewaxing whereby the greatest amount of K wax will be crystallized at a certain temperature.

Still another object of my invention is to provide a method of crystallization or chilling preparatory to dewaxing whereby crystallization will take place more uniformly.

A further object of my invention is to provide a method of crystallization or chilling preparatory to dewaxing in which an increase in the concentration or proportion of the diluent-solvent-oil component is prevented during the crystalization period, or may even be reduced faster than the shift of the partition of solution accompanving the crystallization and in this way accelerate the precipitation.

Another object of my invention is to provide a method of preparation for dewaxing in` which the rate of crystallization and the type of crystal developed is controlled. Y

In the accompanying drawings, which form part of the instant specification and which are to be read in conjunction therewith;

Figure 1 shows curves illustrating the solvent shifts which occur during the chilling of the diluent-s'olvent oil solution.

Figure 2 illustrates diagrammatically one japparatus capable of carrying out the process of my invention.

Referring to Figure 1, it will be noted that the curves show the percentages of solvent present in the respective oil and wax components of the hydrocarbon being chilled. The'percentage of `crystallization which has taken place is also shown. Referring to curve 1, it will be noted that as the temperature is reduced, the percentage of wax crystallization increases rapidly to a y point which for the oil used in the graph, is about.20 F. At this point, further chilling brings about a little wax crystallization. At a point of about 20 F. the rate of crystallization becomes more rapid until a temperature of about -40 F. is reached, at which point the rate of crystallization drops.l Referring to curves 2 and 3 which show the respective percentages of the solvent in the oil and wax components, it will be noticed that as crystallization progressesfthe percentage of solvent present in the wax component decreases. This decrease in the percentage of solvent in the Wax component 1s accompanied by an increase in the percentage of solvent in the oil component. I have come lto the conclusion that the falling off of the rate of crystallization at the first peak shown on curve 1 is due to the retarding effect of the excess of the diluent.

In general, my inventioncontemplates the removal of the excess of solvent as it is thrown off by the Wax ycomponent to prevent the dilution of the oil component and thus prevent the retardation of crystallization and/or the redissolving of the crystals which are formed by the excess of the diluent.

In carrying out my process, a solvent-diluent which is readily evaporable, such as propane, is added to the oil to be dewaxed. It is to be understood, of course, that the propane is in'a 'liquid form. Propane may be readily liquefied within a normal temperature range at pressures between pounds to 120 pounds per square inch. The propane and the oil under liquefying 'iig-ure.

pressures are heated to insure that a'complete solution is formed. Excess solvent is added at the original blending to give an excess diluent eiect duringthe chilling which is accomplished by heat exchange. From the heat exchanger the solution is delivered into pressure controlled "crystallizers-evaporators Where the concentration is reduced to bring about crystallization of the wax under time, temperature and concentration control. This may be done in one or more "crystallizer-evaporators in stage or steps. The exchanger-Chiller is therefore of a special type to take advantage of the pressure change due to the reduction of the temperature on the solution as it passes counter iiow and in indirect contact for heat exchange with the finished dewaxed oil solution. The rate of chilling is very rapid and the velocity and agitation high. These factors in combination with the excess diluent bring about very little if any crystallization, even though the temperature is reduced below the point where crystals will form if time and concentration were favorable. This makes it possible to deliver to the crystallizer-evaporator a'super-cooled solution. In the crystallizerevaporator the time control, concentration and temperature are adjusted favorably for the promotion of crystallization of the Wax. This step brings about a condition of precipitation which will cause the greatest amount of wax to be crystallized. While the oil diluent-solvent is being chilled by heat exchange, I may, if desired, add solvent. curve l that a dilution of the oil component is not disadvantageous up to about the peak of crystallization. After this point, further dilution retards the formation of crystals so that, if crystallization is to continue, it is necessary that the excess diluent be removed or temperature greatly reduced.

By referring to Figure 1, it will be noted that the percentage of solvent in the oil component remains substantially constant after the peak of crystallization is reached, When oil is chilled according to my process due to the fact that the excess diluent thrown off by the wax component is removed. This is shown by curve 2A upon the Likewise, it will be observed, as shown by curve 3A, that the solvent percentage in the wax component decreases at a fairly constant rate. This is due to the fact that crystallization continues at a fairly constant rate due to the elimination of the retarding eifect of the excess solvent as shown by curve 1A. It will also be noticed that substantially the same point of wax crystallization is reached more rapidly, that is, at a higher temperature by practicing my process than is the case where the solventdiluent is not removed and the excess is permitted to retard the Wax crystallization. The curve shows the typical results of preparing wax crystals of the amorphous type where temperature only is manipulated to bring about crystallization, and is a typical example of the results from lack of consideration and utilization of the physical and chemical factor of concentration of the mother liquor.

The rate at which the excess solvent is to be evaporated is determined by the particular type of oil being dewaxed and the percentage of solvent used initially. Obviously this will vary with different oils, depending upon the type and amount of wax present. The peak of crystallization for the particular oil solution can be determined empirically and it is believed that those skilled inthe ilu-t will be readily ab1e to practice my invention from the disclosure here- J 13 through valved line 14. -'I'he mixture passes through line 15 into mixing tank 16 which may be provided with any suitable agitating means. The solvent oil solution passes through valved line 17, through pre-cooler V19, where it is chilled byheat exchange with the dewaxed oil solution coming from the dewaxing equipment. The chilled solution leaves precooler 19 through line 20 and passes into the first stage evaporator crystallizer 21 where the pressure is'reduced to about 25 pounds, for example, to obtain a chilling to a temperature of about -30` F. The solvent evaporated Vpasses overheadthrough line 22 into the solvent line 23. The chilled solution leaves the evaporator crystallizer through line 24 and passes into the second stage evaporator crystallizer 25 in which the pressure is further reduced to, for example 0 pounds pressure to obtain chilling to a temperature of about -40 F. Here, again, the evaporated solvent passes overhead through line 28 into the solvent line 23. The chilled solvent leaves second stage evaporator ycrystallizer 25 through valved line 26 and passes into tank 27. Solvent from solvent tank 13 passes through line 30 into solvent cooler 31 where a portion of the solvent may be evaporated and removed overhead through line 32 and passed into solvent line 23 to chill the solvent in solvent cooler 31. The chilled solvent leaves solvent cooler through line 33 and passes into tank 27. As pointed out above, at the temperatures existing after chilling, the wax will be insoluble to a slight increase of the solvent. The additional chilled solvent is to lbuild up a gravity diiferential between the wax component and the oil component of the solution., The very low density of the diluent and the low percentage thereof remaining in the wax permit me to create-a' gravity gradient ,allowing separation to be made bymeans of centrifuging in a centrifuge such as the Sharples Super-X Tractor.

It is to be noted that my process differs. sharply from that of the priorart in this respect inasmuch as in prior art centrifuging dewaxing methods, the processes depend upon the amorphous wax or a wax structure which is mobile and fluid under pressure. Conventional centrifuging processes will not operate to separate crystalline wax. i

.The chilled-solution leaves tank 2'7 through line 34 and passes to the dewaxing equipment 35 which may be of any suitable type. I may employ a centrifuge as pointed out above or, if desired, a filter or a combination of a centri-av fuge and a filter. The dewaxed -oil solution leaves the dewaxing equipment through line 36V and passes through precooler 19 to chill the in- Durpose of adding many advantages.

the Sharples Super-X Tractor.

coming solution. 'I'he .crystalline wax is removed through line 37.

The solvent recovered in line- 23 is compressed in compressor 38, cooled in cooler 39, and passed through line 40 into solvent tank 13 for re-use in my process.

In practicing my process, the rate of evaporation can be readily controlled by pressure regulation, it being obvious that a reduction of pressure will permit an increased evaporation to take place. The amount of pressure reduction governs the rate of evaporation.

It will be appreciated that my method has I am enabled to obtain a substantially complete crystallization at a higher temperature than has heretofore been possible. The process can be conducted at a much more rapid rate and the type of crystals which will be formed will enable a more complete andV effective wax separation to take place. This is due to the fact that, after the wax crystals have been redissolved by an excess of diluent, as in conventional systems, a softer crystal is formed and that portion of the Wax which is crystallized after the rst peak of crystallization is reached is not as large or as firm as those crystals which are formed during the initial stages vof crystallization. Furthermore, after the wax has been dissolved a considerably lower temperature is necessary to effect complete crystallization. This is not only expensive,but requires more time.

After the wax crystal as desired has been de- Veloped` and slightly super-chilled, then I may add additional diluent which has been cooled to the same temperature of the solution, and underE this condition the wax will be insoluble to a slight increase indiluent; and in this way I can build up a gravity differential between the wax component and the oil component of the solution or mixture. Due to the very low density of the diluent and the low percentage of diluent left in the wax, I am able' to create agravity difference that will allow centrifugation with a basket type centrifugal Asuch as This wil1 be noted to be different from the conventional centrifugal dewaxing which is dependent upon amorphous wax orv a wax structure that is mobile and iiuid under pressure. 'I'he conventional centrifugal process will not separate crystalline waxes.

Having thus described my invention, what I claim is:

1. A process of crystallizing wax in hydrocarbon oils, including the steps of admixing a liquefled normally gaseous solvent with a wax-bearwax precipitating temperature, continuing the cooling step and simultaneously removing a portion of the solvent from the solution as rapidly as it is freed from the wax to such extent that the percentage of solvent in the oil component is maintained substantially uniform.

2. A processof crystalli'zing waxin hydrocarbon 'oils including the steps of admixing a normally gaseous solvent with a wax-bearing oil,

`ing oil, cooling the solution to a predetermined cooling the solution to a predetermined waxprecipitating temperature, continuing the cooling step and simultaneously removing a portion of the solvent from the solution by evaporation as rapidly as it is freed from the Wax to such extent that the percentage of solvent in the oil component is maintained substantially uniform.

3. A process of crystallizing waxin hydrocarbon oils including the steps of admixig a normally gaseous solvent with a wax-bearing oil, cooling the solution to a predetermined wax precipitating temperature by indirect heat exchange, continuing the cooling by evaporation of a portion of the solvent as rapidly as it is freed from the Wax component to such extent that the percentage of solvent in the oil component is kept substantially uniform after said predetermined temperature is reached.

4. The method of dewaxing hydrocarbon oils comprising the steps of admixing a normally gaseous solvent With a wax-bearing oil, chilling the solution to allow a wax crystallization to take place, controlling the percentage of solvent in the oil component during the chilling step by reducing by evaporation the amount of the solvent as rapidly as it is freed'from the Wax to substantially prevent afretardation of crystallization by the presence of an excess of the solvent, and subsequently separating the Wax crystals thus formed from the solution.

5. A process of dewaxing hydrocarbon oils in which a Wax-bearing oil is diluted with a liqueed normally gaseous solvent and chilled including the steps of chilling the wax-bearing oil solution to a Wax-precipitating temperature and controlling the oil-solvent ratio during the chilling step by reducing by evaporation the amount of the solvent as rapidly as it is freed from the wax to such extent that the percentage of solvent in the oil component is maintained substantially uniform. .f

6. A process f dewaxing hydrocarbon oils including the steps of chilling the wax-bearing oil solution to a wax-precipitating temperature and admixing the oil to be' deWaxed with liquid propane, chilling the solutionto a predetermined Wax precipitating point by evaporating propane therefrom, adding additional liquid propane during said chilling step to Wash the oil from the Wax crystals and to increase the solvent percentage in the oil component, continuing to evaporate propane at a rate to keep the increased propane percentage in the oil component substantially uniform and to further chill the solution.

7. In a process for dewaxing hydrocarbon oils, wherein the Wax bearing oil is diluted with a light, low boiling, normally gaseous hydrocarbon diluent, under such temperature and pressure conditions that the diluent is in the liquid state; chilled by heat exchange with cold, dewaxed oil, further chilled by evaporation of a portion of the diluent, separated from the wax precipitated by the chilling operation, and thereafter passed n heat exchange relation with diluted, undewaxed oil, the method of enhancing the crystallization of the Wax which consists in reducing by vaporization the amount of free diluent as rapidly as it EARL PET'I'Y. 

